1. Field of the Invention
This invention relates generally to a machine executed method and a system for managing one or more data volumes stored outside of an automated storage data library. More particularly, the method and system allow for an efficient handling of transient data storage mediums containing such data volumes that are requested for data processing without displacing data storage mediums stored in the library.
2. Description of the Related Art
Modern computer systems require large quantities of storage capacity. To meet this requirement computer memory is available in many forms. A fast, but expensive, form of memory is main memory, typically in the form of micro chips. Other available forms of memory, known as peripheral memory, include magnetic direct access storage devices (DASD), magnetic tape storage devices, and optical recording devices. Each of these other types of memory has a greater storage density and lower cost than main memory. However, these other memory types require mechanical movement to access stored data and therefore exhibit slower access times than purely electronic main memory.
Storing all data in a computer system in main memory is too costly; but, storing all data on one peripheral storage device reduces performance. Thus, a typical computer system includes both main memory and one or more types of peripheral memory arranged in a data storage hierarchy. In such a hierarchy, main memory is often referred to as the primary data storage. The next level of a hierarchy is known as the secondary data storage, and so on. Generally, the highest level of the hierarchy has the lowest storage density capability, the highest performance, and highest cost. As one proceeds down through the hierarchy, storage density generally increases, performance generally decreases, and associated costs generally also decrease. By transferring data between different levels of the hierarchy, as required, the cost of memory is minimized and performance is maximized. Data is thus stored in main memory only so long as it expected to be required by the processor.
Therefore, in order to have the required information available on an "as needed" basis, much storage at the lowest level of the hierarchy is required. Many business applications, for example, require numerous disks or tapes to meet the lowest level storage needs. Automated storage libraries have been developed to manage the storage of and provide efficient access to such disks or tapes. Automated storage libraries include a plurality of storage bins or slots for retaining data storage media, such as magnetic tapes, magnetic disks, or optical disks, and also have a robotic picker mechanism, and one or more drives. Each data storage medium (DSM) may be contained in a cassette or cartridge housing for easier handling by the picker.
Referring to FIG. 1, a machine readable label to be placed on a DSM is shown. When a DSM is added to the library through an input window, the machine readable bar code label is typically scanned by a laser optical system to discern the bar code data. In this way, a catalog entry may be made based on the bar code data. This bar code data typically contains a volume serial number (VOLSER) in machine readable form as shown by bars 15a. It is well known to use varying widths of bars to designate different information and the use of such bar codes is quite common. It is the VOLSER which is used by the host system to request data residing on a particular DSM. Typically, the label also contains human readable information 15b so that an operator may also identify a particular DSM. Once the process has been initiated to add a DSM to the library, the picker may be automatically commanded to move the DSM to a storage bin. Further, the picker operates on command to transfer the storage media between the storage bins and the drives without manual assistance.
Once a data storage medium is mounted in a drive, data may be written to or read out from that medium for as long as the system so requires. The data stored on the medium is referred to as a "data volume" or simply a "volume". It is conventional in the art to refer to the medium as simply a "volume", once it has data written on it, and this convention is adopted here. In an automated data storage library, the normal operation is to automatically move a data storage medium (DSM) from an internal storage bin, mount it on a medium drive, perform a host requested read/write operation, demount the medium from the drive, and return the medium to the storage bin. The medium remains in the bin until requested again. However, automation hardware is very expensive and space in the library is usually very limited. Therefore, it is common to provide a storage shelf outside of the library for storing DSMs which are not frequently used. Occasionally, these less frequently requested mediums are needed for such operations as updates to the data stored on the medium. In this case, the typical user must mount these mediums on drives outside of the library or insert the medium into the library. DSMs which are placed into an automatic storage library on such a temporary basis are known as "transient data storage mediums" (TDSMs). If a TDSM is placed into a storage bin in an automatic library, it will probably be necessary to remove more frequently used cartridges until the transient mediums have been adequately serviced by the host requested read/write operation.
It is desirable to treat TDSMs differently than DSMs so that they are automatically recognized as not belonging to the library so that precious resources in the library are not allocated to TDSMs except on a temporary basis. Accordingly, it would be helpful to not require machine readable labels for TDSMs so that they are not automatically added to a library cataloging system. Also, the labor burden of adding such a label to a TDSM would be circumvented. However, it would also be desirable to ignore such a label if one is encountered on a TDSM to avoid creating superfluous data. Further, a request from a host to process data residing on more than one TDSM should be efficiently handled without the requirement for machine readable labels being read.
Several automated storage libraries are known. IBM Corporation introduced the 3850 mass storage subsystem for retrieval of magnetic tape modules in the 1970s. More recently, several automated storage libraries for magnetic tape cartridges and optical disks have been introduced. Examples of an automated storage and retrieval system, employing an automated tape cartridge library can be found in U.S. Pat. Nos. 4,864,511 and 4,864,438. Examples of optical disk libraries can be found in U.S. Pat. Nos. 4,974,156 and 4,945,428. Also systems for general automated libraries capable of handling either tapes or optical disks are described in U.S. Pat. Nos. 5,121,483 and 5,197,055. The robotic picker mechanisms of these libraries include one or more grippers. Each gripper is capable of handling one data storage medium at a time.
U.S. Pat. No. 4,864,438 describes an apparatus for managing movement of tape cartridges in an automated tape cartridge library system. In the apparatus, each tape cartridge stored in the library system is identified and its physical location is determined, whether in its home position or in transit. The apparatus includes a path selection apparatus to manage the movement of the tape cartridges between home (storage) positions and mounting positions in designated drives. In this regard, a path between two end points is selected, and the apparatus is reserved to transport the designated tape cartridges between these two end points. Provision is made for maintaining the apparatus reservations until the movement of the tape cartridge is completed. In this fashion, if the movement of the tape cartridge is blocked somewhere along the path, the apparatus remains reserved to return the designated cartridge back to its original or home position. However, this patent does not disclose a solution to the problem of handling TDSMs without requiring the displacement of mediums stored in the library.
Several U.S. Patents disclose techniques useful in an automated library or automated storage system for efficiently handling volumes of data within the library or system, but none address the problem of efficiently handling TDSMs. For example, U.S. Pat. No. 5,197,055 discloses the preemptive demounting of a data volume from a device, such as a tape drive, when the volume has not been accessed by the host in a predetermined period of time and the device has been requested for use by the host. For another example, U.S. Pat. No. 5,121,483 discloses a method of temporarily demounting an optical diskette from a drive so that the drive can be used by another mount request while maintaining an appearance to the host that the demounted volume is still mounted. In yet another example, a method for ejecting cartridges from an automated optical storage library according to the results of employing a well known "least frequently used" algorithm is disclosed in U.S. Pat. No. 4,987,533.